Fixes bug introduced in e819866

Table of content was made unavailable regardless of whether one was
provided by the page or not. This commit fixes this issue by making an
unavailable TOC only if one is not provided by the web page, otherwise
the TOC will be available.

web/dart/reorganize_html.dart

@@ -63,10 +63,11 @@ Future<void> reorganizeHtml() async {
   linkifyImg();
 
   // Add correct class to TOC
-  final toc = (querySelector('#table-of-contents') ?? Element.div()
-    ..attributes['id'] = 'table-of-contents')
-  ..classes.add('dropdown')
-  ..innerText = "Table of Contents Unavailable";
+  final toc = (querySelector('#table-of-contents') ??
+      (Element.div()
+        ..attributes['id'] = 'table-of-contents'
+        ..innerText = "Table of Contents Unavailable"))
+    ..classes.add('dropdown');
   querySelector('#toc-drop').append(toc);
 
   // Remove all <br> tags from HTML